1. Field of the Invention
The present invention relates to a vapor delivery system and method of use, and more particularly, to a delivery system for vaporized liquids, solids or low vapor pressure gases at sub-atmospheric pressures for use in metalorganic chemical vapor deposition (MOCVD) and chemical vapor deposition (CVD) processes.
2. Description of the Related Art
MOCVD and CVD have been extensively used for preparation of films and coatings in semiconductor wafer processing. These deposition processes are favored because of their ability to provide highly conformal and high quality films, at relatively fast processing times. Further, these deposition processes are beneficial in coating substrates of irregular shapes including the provision of highly conformal films even with respect to deep contacts and other openings.
In general, CVD techniques involve the delivery of vapor phase reactants to the surface of a substrate where chemical reactions take place under temperature and pressure conditions that are favorable to the thermodynamics of the desired reaction. Some of the gases utilized for CVD techniques originate as liquids or solids and must be evaporated and transported in their vapor state to the reaction chamber.
The type and composition of the layers that can be formed using CVD is limited by the ability to deliver the reactants or reactant precursors to the surface of the substrate. Typically, in a liquid/solid delivery system, a carrier gas is passed through a vaporizing vessel containing a low vapor pressure material. The carrier gas dissolves the material and transports the vapors to the reaction chamber. The carrier gas is typically bubbled at a controlled rate through the storage vessel so as to saturate the carrier gas with vaporized reactant and the saturated carrier gas is then transported to the reaction chamber.
However, if the low vapor pressure material is a solid material, the carrier gas can bore a hole thru the bulk material, such that, the carrier gas tunnels thru the solid material and ultimately does not maintain a consistent concentration. This can cause inconsistency in flow rates of a vaporized source material because the consistency of flow is dependent on sufficient contact of the carrier gas with the liquid or solid source materials. When inconsistencies in the flow rate occur, the flow rate and temperature can be increased but at the cost of reduced lifetime of the system. Further, additional analytical instruments must be included in the system to assure that the correct concentration is being introduced into the reaction vessel.
Accordingly, there is a need in the art for a delivery system that efficiently vaporizes solid and/or liquid precursor materials without the disadvantages of the prior art, such as condensation of vaporized precursor in the lines connecting the vaporizing chamber to the processing chamber, inconsistent vapor flow to downstream deposition systems resulting from tunneling of the carrier gases upon extended contact with the precursor material, and/or additional operating costs due to installation and maintenance of additional valves and analytical tools.